Embodiments of the present invention generally relate to semiconductor device manufacturing. Specific embodiments pertain to temperature distribution measurements during thermal processing as an indication of process uniformity.
Typically, process quality assessment on a rapid thermal processing (RTP) tool consists to a large part in processing expensive, high quality monitor wafers that need to be analyzed using metrology tools like 4-point probes for sheet resistance, or ellipsometers for film thickness. By running the production recipe, the sheet resistance variation across the monitor wafer can be measured and it can be assumed that this is representative for the uniformity of any product wafer. By optimizing the process parameters, the resistivity variation of the monitor wafer is minimized, which would result in the best possible uniformity also on all product wafers. To ensure production yield, sample monitoring may be performed each shift or each day.
However, the use of monitor wafers has the tendency of being either expensive or inaccurate and it assumes and relies on a perfectly stable processing situation. With more aggressive thermal processing requirements, i.e. faster ramp rates, minimal time at temperature, and higher demands for uniformity and repeatability new approaches are needed. In RTP, the variability of the thermal properties of wafers challenges the controlled performance of the system. There is an increased need to address the smaller scale variability within the wafer during thermal processing. In addition, RTP may involve application of a heating spike over a finite duration on a rotating substrate. Direct temperature measurements reflect changing temperature as a result of a spike and/or of a directional (rotational) effect, and therefore may not immediately reveal if a process is stable or uniform without applying a metrology on a wafer, which may be a monitor wafer.
Therefore, there is a need to provide novel and improved methods and systems for temperature measurement that can determine uniformity of an RTP process based on in-process measurements of temperature and other directly measurable in process phenomena without the exclusive use of monitor substrates.